Thank you for the answer!
I use a an old german software from 2009 called "Digitale Bibliothek". When I search through a book it shows me the searched term in the structure of the book. I can export the file to epub with the structure. The book in the image has 14.000 pages, to have a good overview is crucial. The library has over 400 volumes of books including images, you can search through all of them in seconds.
